On pages X–XI of his preface to "L. Feuerbach" (1905 edition), Plekhanov says:

"One German writer remarks that for empirio-criticism, experience is only an object of investigation, and not at all a means of cognition. If this is so, then the opposition of empirio-criticism to materialism loses its meaning, and discussions on the theme that empirio-criticism is called upon to replace materialism turn out to be completely empty and idle."

This is nothing but utter confusion.

Fr. Carstanjen, one of the most "orthodox" followers of Avenarius, says in his article on empirio-criticism (a reply to Wundt), that "for the 'Critique of Pure Experience,' experience is not a means of cognition, but only an object of investigation"[91]. It turns out, according to Plekhanov, that the opposition of Fr. Carstanjen's views to materialism loses its meaning!

Fr. Carstanjen almost literally paraphrases Avenarius, who in his "Remarks" decisively opposes his understanding of experience, as that which is given to us, which we find (das Vorgefundene) – to the view of experience as a "means of cognition" "in the sense of the dominant, in essence thoroughly metaphysical, theories of cognition" (1. c., S. 401). The same thing is said following Avenarius by Petzoldt in his "Introduction to the Philosophy of Pure Experience" (vol. I, S. 170). It turns out, according to Plekhanov, that the opposition of the views of Carstanjen, Avenarius, and Petzoldt to materialism loses its meaning! Either Plekhanov did not "finish reading" Carstanjen and Company, or he took his reference to "one German writer" from fifth-hand sources.

What then does this assertion of the most prominent empirio-critics, misunderstood by Plekhanov, mean? Carstanjen wishes to say that Avenarius in his "Critique of Pure Experience" takes experience as the object of investigation, that is, all manner of "human statements." Avenarius does not investigate here – says Carstanjen (S. 50 of the cited article) – whether these statements are real or whether they pertain, for example, to apparitions; he merely groups, systematizes, formally classifies all possible human statements, both idealistic and materialistic (S. 53), without entering into the substance of the matter. Carstanjen is entirely right in calling this point of view "skepticism par excellence" (S. 213). Carstanjen defends, among other things, in this article his dear teacher against the shameful (from the perspective of a German professor) accusation of materialism hurled by Wundt. What sort of materialists are we, forgive me! – such is the sense of Carstanjen's objections – if we speak of "experience," it is not in that ordinary, current sense which leads or could lead to materialism, but in the sense of our investigation of everything that people "state" as experience. Carstanjen and Avenarius regard the view of experience as a means of cognition as materialistic (this may be the most usual view, but it is nonetheless incorrect, as we have seen from the example of Fichte). Avenarius cuts himself off from that "dominant" "metaphysics" which stubbornly regards the brain as the organ of thought, disregarding the theories of introjection and coordination. By what we find or what is given to us (das Vorgefundene), Avenarius understands precisely the indissoluble connection of the I and the environment, which leads to a confused idealistic interpretation of "experience."

Thus, under the word "experience," undoubtedly both a materialist and an idealist line in philosophy can be concealed, as well as both a Humean and a Kantian one, but neither the definition of experience as an object of investigation[92], nor the definition of it as a means of cognition, resolves anything in this respect. Carstanjen's remarks against Wundt, specifically, have absolutely nothing to do with the question of the opposition of empirio-criticism to materialism.

As a curiosity, we note that Bogdanov and Valentinov, in their reply to Plekhanov on this point, displayed no better familiarity. Bogdanov declared: "not entirely clear" (III, p. XI), "it is the business of empirio-critics to sort out this formulation and accept or not accept the condition." A convenient position: as it were, I am not a Machist, and I am not obliged to sort out in what sense some Avenarius or Carstanjen speaks of experience! Bogdanov wishes to make use of Machism (and Machist confusion with "experience"), but does not wish to answer for it.